Fix MultisampledRenderingWithDepthTest

Comments

Fix MultisampledRenderingWithDepthTest
This test was using two separate depth-stencil textures for sequential
render passes. The second render pass is supposed to load the texture
from the first but it was instead loading a new uninitialized texture.
Bug: dawn:133
Change-Id: I615ec4502a6f26bd039187b0c1942ffbb806b549
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/6640
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>